Caption: Artist's impression of the space-based "railgun" or "hypervelocity launcher" planned as part of the American government's "Star Wars" programme, or Strategic Defense Initiative. The railgun would employ electrical forces rather than chemical propellants to fire "smart" (intelligent) projectiles. The gun may be able to fire projectiles at velocities of more than 32 km per second, compared with 8 km per second for chemical rockets. The railgun would be used to intercept and destroy missiles as they leave Earth's atmosphere. Several contractors have preliminary designs for such a railgun; this artist's impression was produced by Boeing.